US Patent Publication 20150246183 (Kavokin) titled “Needle-free Injection Devices, Systems and Methods” discloses the theory of using negative pressure to draw the epidermis upward to facilitate injection.
During proto-type development and testing, problems of repeatability were encountered, which are hereinafter addressed. The problems of repeatability arose due to the differences between people. Some persons have a tight epidermis and some persons have a relatively loose epidermis. Some persons are small or underweight, and some persons are large or overweight. Even on the same person the properties of the epidermis may differ on different parts of their body.